The low voltage circuit breaker is a low voltage electric appliance having protective function and performing on/off between an input end and a load end of a main circuit, and at least comprises a contact system performing on/off of the main circuit, an operating mechanism controlling the contact system to perform on/off, a terminal strip for connecting the circuit breaker with the input end and the load end of the main circuit and a housing for installing the operating mechanism, the contact system and the terminal strip; the contact system further comprises a movable contact, a stationary contact and a support shaft parts, the movable contact is installed on the support shaft parts and performs closing/opening with the stationary contact along with the movement of the support shaft parts. The support shaft parts is connected with the operating mechanism and moves along with the control of the operating mechanism. There are two types of contact system, i.e. the double-breakpoint contact system and the single-breakpoint contact system. Each pole of the double-breakpoint contact system has two movable contact points, which are connected in series, and two stationary contact points, which are connected to the input end and the load end of the main circuit respectively, while each pole of the single-breakpoint contact system only has one movable contact point and one stationary contact point. The contact system of the single-pole circuit breaking unit only has a group of the movable contacts and the stationary contacts, while the multi-pole circuit breaker has a plurality of groups of the movable contacts and the stationary contacts, and the number of the groups of the stationary contacts is equal to that of the poles of the circuit breaker.
The double-breakpoint contact system has higher breaking ability than the single-breakpoint contact system, the current is broken at two serial contacts of the circuit breaker, each contact bears low mechanical and thermal stresses and includes two serial arc voltages so as to enhance the breaking ability, therefore, the double-breakpoint contact system is widely applied to moulded case circuit breaker. But for the single-pole circuit breaking units of the double-breakpoint contact system, the following problem needs to be addressed: how to realize balanced mechanical contact pressure between two pairs of the movable contacts and the stationary contacts, otherwise, the electric conductivity of the circuit breaker will be reduced. The Euro Patent EP0314540 discloses a single-pole circuit breaking unit, which is characterized in that: a support shaft parts is a rotation axis; a movable contact having two contact points is installed on the rotation axis; a central point between the two contact points overlaps the center of the rotation axis in order to maintain the moving tracks of the two movable contact points symmetrical; the contact pressure between the two movable contact points and stationary contact points is provided by the spring in order to address the problem that the contact pressure of two groups of contacts of the single-pole circuit breaking unit is distributed unevenly. The Patent EP0314540 has the defects that: the revolving precision of the rotation axis is quite inferior; and the problem that the rotation axis system is stable and suitable in the multi-pole circuit breaker system is not taken into consideration.
The rotation axis in the multi-pole contact system is long in extension, obvious twist is formed as the rotation axis is stressed during revolution so that the movement of the movable contact far away from the center circuit breaker is quite late, which dramatically aggravates the problem of unbalanced contact pressure of the contacts at all poles. Furthermore, the contact system at each pole of the multi-pole circuit breaker needs to be installed and isolated in an independent extinguishing chamber as required by arc extinguishing, so a plurality of groups of the movable contacts cannot be installed in respective extinguishing chamber before the rotation axis equipped with a plurality of groups of the movable contacts penetrates through partitioning walls of the extinguishing chambers, accordingly, it is quite apparent that this brings great difficulty to the design of the supporting structure of the rotation axis, and further, the technical difficulties including complex supporting structure of the rotation axis, difficult installation and debugging and the like are caused.
The invention patent with the application number CN200710151603.1 provides a technical proposal different from the present invention, which is characterized in that: a rotation axis assembly consists of a plurality of support shaft parts, a rotation axis and a rolling bearing and is installed through the rolling bearing thereon as well as a bearing pedestal and a bearing cover plate on a partitioning wall inside a housing of the multi-pole circuit breaker. This proposal can raise the moving precision and flexibility of the rotation axis assembly greatly, however, there are two limitations: 1, according to this proposal, the rotation axis is stabilized only by means of the partitioning wall, so the rotation axis assembly cannot be installed and supported on the partitioning wall of the circuit breaker stably without the cooperation of the bearing cover plate, in this way, the installation precision is unsatisfactory, the debugging is complex and the production efficiency is impacted; and 2, in order to guarantee the supporting stability and precision, this technical proposal fails to be applicable to the multi-pole circuit breaker consisting of a plurality of independent splitting single-pole circuit breaking units, but only to the multi-pole circuit breaker with an integrally structured housing, namely the single-pole circuit breaking units divided by the portioning walls.
The multi-pole circuit breaker consisting of independent splitting single-pole circuit breaker units is advantageous for the optimization of industrial production efficiency and the reduction of production cost, and the circuit breakers with different number of poles can be manufactured only by adopting one production line, one set of moulds and one part since every single-pole circuit breaker unit is universal for the circuit breakers with different number of poles. However, the independent splitting single-pole circuit breaking units need to be controlled by the same operating mechanism in order to perform on/off and tripping operations, hence, new difficult problem is brought to the design of the supporting and drive structures of the rotation axis.